Tests the hypothesis that a direct consequence of muscular inactivity in man is decreased skeletal muscle protein synthesis and that activity related modulation of protein synthesis is mediated via changes in local production of insulin-like growth factor I (IGF-I). The protein synthetic rate in skeletal muscle will be directly measured in normal volunteers subjected to absolute bedrest for seven days. Molecular biology techniques will be employed to quantitate alterations in skeletal muscle messenger RNA and IGF-I.